Consulting-Specifying Engineer - July 2008 - (Page 60)

Equipment Lifecycles Selecting and maintaining smoke detectors Fire and life safety engineers can avoid common problems by properly designing, installing, and maintaining ionization and photoelectric smoke detectors. BY AJ SEVAST, SET, Consultant, RJA Group, Greenwood Village, Colo. moke detectors can have a lifecycle of up to 20 years if certain design and installation recommendations are followed and if annual maintenance is performed for each detector. Given the tight budget of many companies in today’s economy, a reliable fire system can be one less budget issue and one less concern for the owner, operator, or lessee. Generally, when fire systems fail, it is due to lack of planning and maintenance. The following describes common problems associated with detectors that can be avoided at different phases of fire system design, installation, and maintenance. Consider the application When smoke detection devices are selected for a project, the type of detection must be suitable for the application. Ionization and photoelectric smoke detectors commonly are used in many applications. Both detectors have detection limitations, however. The ionization smoke detector is not as effective at detecting flaming fires, while the photoelectric smoke detector is not as efficient with smoldering fires. Therefore, the fuel loads and fire scenarios must be considered before a detector type is chosen. If the wrong detector is selected for an application, the lifecycle of the detector can be shorter or negligible if the detector is rendered useless and needs to be replaced with the right detector. Environmental issues Environmental issues such as altitude, temperature range, humidity, and air contamination need to be considered when selecting detector types. The ionization detectors are S limited to installation at altitudes as high as 3,000 ft above sea level. If they are installed at higher than 3,000 ft above sea level, the detectors often create nuisance alarms and may affect detector responsiveness. The photoelectric smoke detector does not have an altitude limitation. Both detector types can be affected by temperature range and humidity. When detectors are installed where temperatures are below 32 F, ice crystals or condensation can appear inside the sensing chambers and cause the detector to become overly sensitive or create nuisance alarms. At temperatures above 100 F, the detectors’ internal electronic components may not function properly. In humid areas, water droplets can accumulate inside the sensing chamber and affect detector sensitivity, which could create nuisance alarms. Both smoke detectors can be affected by dirty environments, combustion particles, caustic vapors, gas, and fumes that may lead to maintenance issues and nuisance alarms. If air contamination is inevitable, then heat detection may be a better solution for the area in question. It is important to understand the environment a detector is protecting in order to select the correct detector type and increase the lifespan of a smoke detector. Placement and location The efficiency of ionization or photoelectric smoke detectors to detect smoke conditions can be adversely affected if obstructions, ceiling heights, and types of ceiling are not considered when determining their locations. Both detectors are capable of providing 900 sq. ft (30x30 ft) of coverage. 60 Consulting-Specifying Engineer • JULY 2008

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Consulting-Specifying Engineer - July 2008 Contents Viewpoint Letters News M/E Roundtable 40 Under 40 Using Demand-Based Reset Strategies VFDs and Motors: Making the Right Match Grounding and Bonding Practices for Hazardous Areas Codes & Standards Case Study New Products Equipment Lifecycles Advertiser Index Green Space

Consulting-Specifying Engineer - July 2008

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